This invention relates to valve mechanisms preferably for internal combustion engines and, more particularly, to such valve mechanisms having pressure medium supply passages.
Heretofore, certain valve mechanisms for internal combustion engines, particularly for the intake valve, have included a cup-shaped plunger providing a contact surface for a valve control cam and a device for controlling the distance between the contact surface and the free end of the valve stem. Among devices affecting the distance between the cup plunger contact surface and the free end of the valve stem, for example, are hydraulic devices for varying the opening time of the valve as a function of the engine speed or of the load at a given time, or for compensating valve play, or damping devices that prevent hard impact of the valve member upon its seat during closing of the valve.
One valve mechanism of this type is disclosed by German Offenlegungsschrift No. 3004396 wherein the free end portion of a valve stem protrudes into the end of a guide sleeve facing the valve which sleeve contains a piston of a device for controlling the distance between the valve stem and the cam. In that arrangement, the closing spring of the valve extends outside the guide sleeve between a spring disk on the valve stem and a shoulder in a recess of a cylinder head containing the valve with the cup-shaped plunger an the guide sleeve. The closing spring has a larger diameter than the guide sleeve thus requiring a relatively long structure for the valve and valve mechanism.
In addition, a supply passage for a pressure medium such as oil is incorporated in the guide sleeve in the form of an annular passage so that the wall thickness of the guide sleeve is constant around its entire periphery. The guide sleeve at its end near the camshaft is enclosed by the cup plunger at the camshaft end, forms a housing with a connecting nozzle accommodating a hydraulic device to compensate for play and a throttling device for hydraulic control of the valve actuation times as a function of the engine load.
The prior art also describes hydraulic devices for controlling valve times as a function of rotational speed. In U.S. Pat. No. 3,967,602, such a device includes an orifice in the face of the cup plunger forming the contact surface for the cam and the flow of oil through the orifice is greater at low speeds than at high speeds, causing the opening time of the valve to be less at low speeds than at higher ones.